Hazardous substances (e.g., toxic/noxious gasses and/or harmful particulates) may be present in the air in a building (e.g., a house). Exposure of a building occupant to hazardous substances may be harmful to the occupant's health. Detectors may be used to determine instantaneous levels of various hazardous substances. Mere knowledge of instantaneous levels of hazardous substances, however, does not quantify the cumulative exposure of the occupant to the hazardous substances, and therefore may not provide a useful indication of the health risk to the occupant.